Process for the production of an electrophotographic liquid developer containing gelatin

ABSTRACT

A process for producing a liquid developer for developing electrostatic latent images which comprises (1) adding to an aqueous solution of gelatin, the concentration of the gelatin being in the range of approximately 1 to 20 percent by weight, an alcohol in an amount less than that of causing the precipitation of gelatin to provide a solution of gelatin in a water-alcohol mixed solvent, (2) dispersing the solution thus prepared in an organic solvent which is miscible with water but is a non-solvent for gelatin to form a dispersion of fine gelatin particles where the amount of said organic solvent is at least 10 times the amount of the mixed gelatin solution of water and alcohol and recovering the fine gelatin particles from the dispersion, and (3) dispersing the fine gelatin particles thus recovered in a carrier having an electric resistance of higher than 101010 Omega cm.

United States Patent 1 1' Tamai 1 1 Feb. 27, 1973 Inventor: Yasuo Tamai, Asaka-shi, Japan [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: Feb. 5, 1970 [21] App]. No.: 9,042

[30] Foreign Application Priority Data Feb. 5, 1969 Japan ..44/8517 [52] US. Cl. ..252/62.1, 106/125, 106/135, 260/117, 96/12 [51] Int. Cl. ..G03g 9/04 [58] Field of Search ..252/62.1; 260/8, 117; 117/372 X; 96/1, 97, 98; 106/125, 135

[56] References Cited UNITED STATES PATENTS 3,682,825 8/1972 Tamai et a1 ..252/62.1 3,137,630 6/1964 Hecker et al. ..117/

3,558,756 l/l97l Aldridge ..106/ 3,357,830 12/1967 Bixby ..96/1.2 2,527,268 10/1950 Hart et al. ..96/97 2,297,691 10/1942 Carlson ..96/l 2,197,843 4/1940 Leeuwen.... ..l06/135 2,105,413 1/1938 Dewsbury... ..106/l35 1,854,061 4/1932 Pigache ..106/

Primary ExaminerGeorge F. Lesmes Assistant Examiner-J. P, Branner Attorney-Addams & Ferguson [57] ABSTRACT A process for producing a liquid developer for developing electrostatic latent images which comprises (1) adding to an aqueous solution of gelatin, the concentration of the gelatin being in the range of approximately 1 to 20 percent by weight, an alcohol in an amount less than that of causing the precipitation of gelatin to provide a solution of gelatin in a water-alcohol mixed solvent, (2) dispersing the solution thus prepared in an organic solvent which is miscible with water but is a non-solvent for gelatin to form a dispersion of fine gelatin particles where the amount of said organic solvent is at least 10 times the amount of the mixed gelatin solution of water and alcohol and recovering the tine gelatin particles from the dispersion, and (3) dispersing the fine gelatin particles thus recovered in a carrier having an electric resistance of higher than 1010"Qcm.

10 Claims, No Drawings PROCESS FOR THE PRODUCTION OF AN ELECTROPIIOTOGRAPIIIC LIQUID DEVELOPER CONTAINING GELATIN This invention relates to a process for producing liquid developer containing gelatin toner adapted for use in developing electrostatic latent image obtained in electrophotographic or electrostatic recording method, and particularly to a process for producing a liquid developer adapted for producing gelatin relief to be employed for color printing process utilizing electrostatic latent image.

Multicolor print of good quality is most widely obtained by silver halide coatings combined with color forming development process. In addition to this, socalled dye transfer or dye imbibition process which utilizes gelatin relief resulting from tanning development of silver halide coatings is also commercially known in the name of Technicolor process, etc.

Although the former process is provided with wider application and is suitable for processing in large quantity, the light-stability and life of obtained image is insufficient. On the other hand the dye transfer process is capable to providing images with extremely good lightstability and long life. This process, having a nature resembling printing method, becomes economical in case of obtaining many copies from one original but is expensive if only limited number of copies is required, because the preparation of gelatin relief requires time and skill. In consideration of this point, the inventor already proposed a color printing process utilizing dye transfer process by means of easily obtainable gelatin relief, which consists of following steps, (cf., Belgian Pat. No. 724,581):

I. forming electrostatic latent image on an electrophotographic or electrostatic recording material:

II. converting said latent image into material image by means of fine powder capable of absorbing aqueous solution of a water-soluble dye solution (for example, gelatin toner);

III. fixing thus obtained visible image by suitable method;

IV. bringing said image into contact with aqueous solution of water-soluble dye thereby causing absorption of dye into said image; and

V. keeping a surface capable of absorbing said dye solution of a separate image-receiving material into face-to-face close contact with said image thereby transferring said absorbed dye to said dyeabsorbing surface to form final copy.

In the preparation of liquid developer containing gelatin powder (gelatin toner) for use in color printing process as explained above, the most difficult step is pulverization of gelatin into sufficiently fine state.

Uniform pulverization is difficult to realize since grain or flakes of gelatin is hard and tenace. On the contrary a liquid phase process in which aqueous solution of gelatin is dispersed in a solvent in which gelatin is insoluble and fine particles of gelatin from thus obtained dispersion involves a drawback of easily causing coagulation of gelatin in premature stage. Furthermore the spray drying method in which aqueous solution of gelatin is sprayed into dry air to obtain pulverized gelatin is incapable of providing particle size sufficiently fine for use as toner in liquid developer for acquiring a good image.

means of Consequently an object of this invention is to provide an improved process for producing liquid developer containing gelatin toner adapted for use in preparing gelatin relief to be utilized in dye transfer process to obtain color print.

Another object of this invention is to provide a process for producing liquid developer for electrophotography containing uniform and fine gelatin particles as toner and adapted for use in electrophotographic color printing process as explained above.

The objects of this invention can be achieved by the process of this invention for producing a liquid developer for electrophotography, which comprises:

1. adding to an aqueous solution of gelatin an alcohol in an amount less than that causing the precipitation of gelatin to provide a solution of gelatin in water-alcohol mixture:

2. dispersing the gelatin solution thus obtained in an organic solvent which is miscible with water but is a non-solvent for gelatin to provide a dispersion of fine gelatin particles and recovering fine gelatin particles from said dispersion; and

3. dispersing gelatin particles thus obtained in a carrier liquid having an electric resistance of higher than 10"Ocm.

Furthermore the present inventor found to be able to achieve a further improved result by inserting, between the steps (2) and (3) of the aforesaid process for producing liquid developer, a step of washing the obtained gelatin powder with a water-miscible organic solvent in which gelatin is insoluble thereby removing moisture containing in said powder.

As to the gelatin, both hide and bone gelatin can be satisfactorily employed for this invention. However, the range of gelling point should not be excessively wide in order to obtain sufficient dispersion.

Purified ordinary photographic gelatin is suitable for use in this invention. In case of preparing aqueous solution of such gelatin, the concentration of gelatin should be between 1 and 20 wt.%, since excessively low will involve the use of large amount of water in above-mentioned step 2 therefore leading to lowering of yield of gelatin with respect to the amount of employed organic solvent, and will also result in the incorporation of large amount of water in the obtained particles of gelatin thereby lowering the efiiciency of additional washing step mentioned above, whereas an excessively high concentration will make it impossible to add a large amount of alcohol in step 1, thus leading to insufficient dispersion and tendency of causing coagulation. At the addition of alcohol to aqueous solution of gelatin, it is preferable to warm these two liquids to 30-40C, since the aqueous solution of gelatin tends to set in cold state. Alcohol to be employed for this purpose may be methanol, ethanol, isopropyl alcohol or glycerine. The amount of alcohol to be added should desirably be 0.1 to 3 parts by volume with respect to 1 part by volume of gelatin solution. Gelatin is insoluble in alcohol, but considerably soluble in water-alcohol mixture. For example, about 1 part of methanol can be added without causing precipitation to 1 part of 5 wt.% aqueous solution of gelatin kept at 45C. A prior process, in which aqueous solution of gelatin is directly dispersed in an organic solvent which is non-solvent for gelatin is inevitably accompanied with a drawback of easily causing aggregation of gelatin. According to this invention, however, it is found that the addition of alcohol to aqueous solution of gelatin without reaching the extent of forming turbidity facilitates dispersion of gelatin and prevents the aggregation of gelatin after said dispersion. As the excessive addition of alcohol will lead to the aggregation of gelatin, said addition should be terminated just before the formation of white turbidity. If the white turbidity arose, transparent liquid could be again obtained by adding the little amount of hot water.

As the water-miscible organic solvent which is nonsolvent for gelatin in the step 2 mentioned above be ketones or alcohols may be used, and acetone, methylethylketone or ethanol is preferable. These organic solvents should be used in a -300 times by volume with respect to that of gelatin solution (dissolved in water-alcohol). The lower limit of this amount is determined by the dispersibility of gelatin since the obtained gelatin particles are apt to aggregate when a too much amount of gelatin solution is used, whereas the upper limit is determined by working efficiency since it is uneconomical because of consumption of large quantity of solution, although the gelatin particles can be sufficiently dispersed in this case.

In the step 2, in order to improve dispersibility of gelatin particles, it is possible to add a small amount of vegetable oil to the water-miscible organic solvent which is non-solvent for gelatin. Also a preferable result can be obtained by adding a surface active agent to said organic solvent. For preparing the dispersion of gelatin solution, the use of ultrasonic stirring is most preferably but a high-speed mixer may be used.

The dispersion of gelatin particles in an organic solvent obtained in step 2 contains a considerable amount of water derived from the aqueous solution of gelatin, a part of which is in the organic solvent phase and a part of which is present in the gelatin particles. The water present in said dispersion should be removed since the presence of water in liquid developer for electrophotography is not preferable. For this purpose gelatin particles in the dispersion are further washed with the aforesaid organic solvent. The gelatin particles present in the dispersion are recovered by filtration, floccuration, centrifugal separation, etc., and then redisperse in the fresh organic solvent mentioned above.

By the step which may be repeated, if necessary, the content of water present in gelatin particles is reduced and simultaneously the gelatin particles shrink to be finer, which results in reducing the tendency of aggromation.

Gelatin particles sufficiently dehydrated by the washing step are collected again by means of filtration, cen

trifugal separation or flocculation and dispersed in a carrier liquid. Although the gelatin particles may be dispersed after drying, much more stable dispersion can be obtained by adding gelatin particles in wet (or paste) state to said organic solvent.

The carrier liquid for use in this invention may be similar to that employed in ordinary electrophotographic liquid developer, namely may be a non-polar organic solvent having a high electric resistance, preferably higher than l0Qcm, since low electric resistance will give rise to the destruction of electrostatic latent image formed on electrophotographic photosensitive layer.

Thus, the examples of the carrier liquid are cyclohexane, kerosene, gasoline, isooctane, heptane, hexane and chlorofluorohydrocarbons. The carrier liquid may contain various components soluble therein, such as nonionic surface active agent, dispersing agent or resin for fixing etc.

The amount of gelatin to be added (concentration of toner) to said carrier liquid should preferably be 0.001-5 percent by weight with respect to said carrier liquid since electrostatic latent image on photosensitive layer cannot effectively be developed when said concentration is excessively low, and an excessively high concentration will result in the formation of fogging. Besides there are instances the stability of dispersion is deteriorated with the increase of said concentration.

By the use of liquid developer containing gelatin obtainable according to this invention, gelatin relief can be prepared by the following steps:

I. forming an electrostatic latent image on an insulating layer of electrophotographic or electrostatic recording layer;

II. developing said image with the liquid developer containing gelatin toner;

III. fixing thus obtained gelatin image by means of suitable method;

IV. bringing thus fixed gelatin image into contact with an aqueous solution of water-soluble dye, thereby said dye being absorbed by said image; and

V. keeping a surface capable of absorbing said solution of a separate image-receiving material into face-to-face contact with said gelatin image thereby, transferring said absorbed dye onto said image-receiving material to form final image.

The steps IV and V represent the procedure of obtaining dye image by means of obtained gelatin matrix, and thus plural copies of image-receiving sheets having dye image can be obtained by repeating the steps IV and V. In the case of electrophotographic photosensitive layer consisting of zinc oxide which generally provides electrostatically negative latent image, the development is carried out by electrostatic attraction since charge of the gelatin toner of this invention is electrostatically positive. On the other hand when selenium which generally provides electrostatically positive latent image is used as photosensitive layer, the development by liquid developer of this invention is carried out by electrostatic repulsion.

As the gelatin toner obtained according to this invention is almost colorless, it is very difiicult to judge the result of development by inspecting visually the developed surface. Consequently it is advantageous to add toner consisting of colored pigment to the liquid developer in a 1/5-l/l00 amount of gelatin toner. It is also advantageous to prepare liquid developer from gelatin particles containing colored pigment or dye.

This invention will be further clarified by the following examples.

Example 1 5 g. of photographic gelatin added to g. of distilled water. After 30 minutes, the gelatin was sufficiently swelled. Thereafter, the mixture was warmed to 60C to provide a transparent aqueous solution of gelatin. While keeping 10 ml. of thus obtained solution at 45C, methanol was added gradually until very slight white turbidity was formed. The amount of methanol added was ll ml. Then when 0.5 ml. of distilled water was added, the white turbid disappeared. Thus, obtained solution of gelatin in water-methanol was dispersed in l l. of acetone by means of ultrasonic stirring to provide a white dispersion of gelatin, which was centrifuged to obtain precipitates consisting of fine particles of gelatin. Said precipitate was immediately dispersed again into 500 ml. of acetone by means of ultrasonic stirring and then centrifuged to precipitate fine particles of gelatin.

Precipitated gelatin thus obtained was sufficiently dispersed in a liquid carrier having the following composition:

cyclohexane 800 ml. kerosene 150 ml. soybean oil 46 ml. varnish obtained by cooking rosinmodified phenol-formaldehyde resin and vegetable oil 4 ml.

Thereby to obtain liquid developer of milk-white color. In this composition soybean oil was employed as dispersing agent. Rosin-modified phenol-formaldehyde resin was used as fixing agent. This agent is soluble in carrier liquid but is insolubilized in rinsing bath (for instance, isoparaffin rinsing bath) used after development thereby fixing gelatin toner. Kerosene was added in order to control the evaporation of liquid developer. Gelatin toner contained in this liquid developer was found to be provided with electrostatically positive charge.

At the same time 100 parts by weight (the quantities are expressed hereinafter in weight) of photoconductive zinc oxide and 20 parts of epoxyester of dehydrated castor oil fatty acid are mixed with an appropriate amount of toluene to obtain homogeneous coating mixture.

This mixture was then added with 0.02 parts of fluorescein and 0.2 parts of tetrabromophenol blue dissolved in a small amount of ethylene glycol monomethylether thereby to extend the photoconductive response of zinc oxide to cover whole range of visible spectrum.

After further addition of toluene, thus obtained solution was applied on an aluminized surface of polyethylene terephthalate film in a thickness of 90p. The thickness after drying was ca. 8p" After sufficient drying in the dark, thus obtained coated material showed satisfactory performance as electrophotographic photosensitive material.

Said material was subjected to negative corona discharge at darkness thereby forming uniform electrostatic charge thereon and then subjected to imagewise projection of a color slide superposed with a red filter.

After exposure, the photosensitive sheet was wetted with kerosene and immediately immersed into the liquid developer explained above. The surface holding latent image may face to the bottom of stainless steel container containing said liquid developer in order to utilize said container as the developing electrode.

After dipping for 90 seconds the sheet was taken out, rinsed with isoparaffin (lsoper E: Esso Standard Oil Co.) and dried;

Thus formed gelatin image was then hardened by dipping said sheet in 1 percent methanol solution of formaldehyde lowed by standing overnight at room temperature.

After hardening treatment, zinc oxide contained in photosensitive layer was almost removed by dipping said photosensitive sheet having gelatin image thereon in 40 percent aqueous solution of acetic acid for 2 minutes.

Thus a gelatin relief for cyan color printing was completed.

A separate sheet material was subjected to imagewise projection through the same color slide superposed with a green filter and processed in the same manner as explained above thereby to obtain a gelatin relief for magenta color printing.

Also the matrix for yellow color printing was prepared by using a blue filter.

These three gelatin reliefs were immersed for 2 minutes into aqueous dye solutions containing Acid Blue 54 (Anthraquinone dye stuff), Acid violet 7 (CI. 18055) and Acid Yellow 23 (CI. 19140) and then washed with a washing bath consisting of aqueous solution of acetic acid.

A dye-receiving sheet provided with a gelatin layer was immersed in aqueous solution of aluminum sulfate and then brought into contact successively in register with said three gelatin reliefs. Dyes absorbed in toner images were thus transferred to said gelatin layer to form a color reproduction of extremely high quality. Said gelatin reliefs were found to be capable of providing at least times run.

Example 2 A selenium layer of 60p, thick was provided on an aluminum plate by vacuum deposition.

Thus formed xerographic plate was subject to positive corona discharge at darkness thereby forming surface charge of 350 V., and then subjected to imagewise projection on a photographic enlarger through a color slide superposed with a red filter.

After exposure, the xerographic plate was wetted with kerosene and immersed into the liquid-developer of example 1. In this case a flat metal plate was held at a distance of 0.2 mm to the surface of said xerographic plate as a developing electrode. So-called reversal development was carried out by applying a bias potential of V. to the xerographic plate. After immersing for 90 seconds, the plate was taken out, washed with Isoper E (lsoparaffin solvent: Esso Standard Oil Co.) and dried.

The obtained gelatin image was hardened by dipping said plate for 20 seconds in 1 percent methanol solution of formaldehyde followed by standing for 5 hours at room temperature, thereby to complete a gelatin relief for cyan color printing.

A gelatin relief for magenta color printing was prepared similarly on a separate xerographic plate by means of exposure through the same color slide and a green filter. Also the gelatin relief for yellow color printing was prepared with a blue filter.

Thus obtained three reliefs were dyed as described in Example 1.

An image-receiving sheet having a gelatin layer was treated as in Example 1, and brought into contact in register successively with said three gelatin reliefs. Dyed obtained in toner images were thus transferred to said gelatin layer to form a positive color reproduction of extremely high quality. Said matrixes were found to be capable of providing at least 25 copies.

The xerographic plates after use were washed successively with warm alkaline aqueous solution acetonetoluene mixture and toluene, and dried. Thus the plates were ready for use again in another cycle.

Example 3 Solution of gelatin in mixed solvent was prepared according to the procedure of Example 1, and employing ethanol instead of methanol. The amount of ethanol added was 10 ml.

Gelatin relief could be prepared by thus obtained similar developer and same procedure as described in Example 1.

Example 4 Methylethyl ketone was employed instead of acetone in the procedure of Example 1. Gelatin relief could also be prepared by thus obtained similar developer and same procedure as described in Example 1.

Example 5 A mixture of 20 ml. of soybean oil and 980 ml. of acetone was employed instead of acetone in Example 1. The obtained liquid developer contained gelatin particles finer than those obtainable in Example 1.

Example 6 Solution of gelatin in mixed solvent was prepared by employing 10 ml. of ethanol instead of methanol in Example 1. Also methylethylketone was used as dispersing agent instead of acetone, thereby to provide a liquid developer similar to that obtainable in Example 1.

What is claimed is:

l. A process for producing a liquid developer for developing electrostatic latent images which comprises:

l. adding to an aqueous solution of gelatin, the concentration of the gelatin being in the range of approximately 1 to percent by weight, an alcohol in an amount less than that of causing the precipitation of gelatin to provide a solution of gelatin in a water-alcohol mixed solvent,

. dispersing the solution thus prepared in an organic solvent which is miscible with water but is a nonsolvent for gelatin to form a dispersion of fine gelatin particles where the amount of said organic solvent is at least 10 times the amount of the mixed gelatin solution of water and alcohol and recovering said fine gelatin particles from the dispersion,

and

3. dispersing the fine gelatin particles thus recovered in a carrier having an electric resistance of higher than l00cm.

2. The process as claimed in claim 1 wherein said alcohol is methanol, ethanol, isopropyl alcohol, or glycerine.

3. The process as claimed in claim 1 wherein the amount of the alcohol is 0.1-3 parts by weight per 1 art b wei ht of elatin solution. p 4. fire pr ocess%s claimed in claim 1 wherein said organic solvent which is miscible with water but is a nonsolvent for gelatin is acetone, methylethyl ketone, or

ethanol.

5. The process as claimed in claim 1 wherein said carrier liquid is cyclohexane, kerosene, gasoline, isooctane, heptane, hexane, or a chlorofluorohydrocarbon.

6. A process for producing a liquid developer for developing electrostatic latent images which comprises:

l. adding to an aqueous solution of gelatin, the concentration of the gelatin being in the range of approximately 1 to 20 percent by weight, an alcohol in an amount less than that of causing the precipitation of gelatin to provide a solution of gelatin in a water-alcohol mixed solvent,

. dispersing the solution thus prepared in an organic solvent which is miscible with water but is a nonsolvent for gelatin to fon'n a dispersion of fine gelatin particles where the amount of said organic solvent is at least 10 times the amount of the mixed gelatin solution of water and alcohol and recovering said fine gelatin particles from the dispersion,

3. washing said gelatin particles thus recovered with an organic solvent which is miscible with water and is a non-solvent for gelatin, and

. dispersing said fine gelatin particles thus washing in a carrier liquid having an electric resistance of higher than l0flcm.

7. The process as claimed in claim 1 wherein said alcohol is methanol, ethanol, isopropyl alcohol, or glycerine.

8. The process as claimed in claim 1 wherein said organic solvent to be employed in the step (2) or (3) is acetone, methyl ethyl ketone, or ethanol.

9. The process as claimed in claim 1 wherein said carrier liquid is cyclohexane, kerosene, gasoline, isooctane, heptane, hexane, or a chlorofluorohydrocarbon.

10. The process as claimed in claim 1 wherein the amount of said alcohol is 0.1-3 parts by weight per 1 part by weight of the gelatin solution.

t l t t 

2. dispersing the solution thus prepared in an organic solvent which is miscible with water but is a non-solvent for gelatin to form a dispersion of fine gelatin particles where the amount of said organic solvent is at least 10 times the amount of the mixed gelatin solution of water and alcohol and recovering said fine gelatin particles from the dispersion,
 2. The process as claimed in claim 1 wherein said alcohol is methanol, ethanol, isopropyl alcohol, or glyceRine.
 2. dispersing the solution thus prepared in an organic solvent which is miscible with water but is a non-solvent for gelatin to form a dispersion of fine gelatin particles where the amount of said organic solvent is at least 10 times the amount of the mixed gelatin solution of water and alcohol and recovering said fine gelatin particles from the dispersion, and
 3. The process as claimed in claim 1 wherein the amount of the alcohol is 0.1-3 parts by weight per 1 part by weight of gelatin solution.
 3. dispersing the fine gelatin particles thus recovered in a carrier having an electric resistance of higher than 1010 Omega cm.
 3. washing said gelatin particles thus recovered with an organic solvent which is miscible with water and is a non-solvent for gelatin, and
 4. dispersing said fine gelatin particles thus washing in a carrier liquid having an electric resistance of higher than 1010 Omega cm.
 4. The process as claimed in claim 1 wherein said organic solvent which is miscible with water but is a non-solvent for gelatin is acetone, methylethyl ketone, or ethanol.
 5. The process as claimed in claim 1 wherein said carrier liquid is cyclohexane, kerosene, gasoline, iso-octane, heptane, hexane, or a chlorofluorohydrocarbon.
 6. A process for producing a liquid developer for developing electrostatic latent images which comprises:
 7. The process as claimed in claim 1 wherein said alcohol is methanol, ethanol, isopropyl alcohol, or glycerine.
 8. The process as claimed in claim 1 wherein said organic solvent to be employed in the step (2) or (3) is acetone, methyl ethyl ketone, or ethanol.
 9. The process as claimed in claim 1 wherein said carrier liquid is cyclohexane, kerosene, gasoline, iso-octane, heptane, hexane, or a chlorofluorohydrocarbon.
 10. The process as claimed in claim 1 wherein the amount of said alcohol is 0.1-3 parts by weight per 1 part by weight of the gelatin solution. 